1. Field of the Invention
The present invention refers to a linear bearing for continuous longitudinal movement, and more particularly to a linear bearing comprising a housing for being moveably supported by rollers on a travel rail, the housing defining a closed roller orbit including a load zone, two reversal regions, and a return travel zone.
2. Description of Related Art
Various linear bearings of this same general type are known and have been used for a long time. In these prior systems, upon movement of the housing with respect to the travel rail, the rolling elements revolve in closed orbit paths. Generally, they roll satisfactorily within the load zone and the return-travel zone. Problems, however, exist in the reversal regions, particularly at the point where the rolling elements leave the load zone. More specifically, at this point the rolling elements have the direction of rotation which they had in the load zone. However, upon reaching the first reversal region, the roller elements encounter a first reversing means for reversing their travel direction. This first reversing means is stationary with respect to the rolling elements, which causes the rolling elements to begin rolling in the opposite direction of rotation. The result is that the rolling elements are first decelerated and then change their direction of rotation, which leads to considerable frictional losses.
The same process is repeated, disregarding the force of gravity, when the rolling members pass through a second reversing means, through which the rolling members pass from the return-travel zone and onto the travel rail and toward the load zone. These difficulties are aggravated by the fact that when in rapid longitudinal movement, the rolling elements, due to their centrifugal force, are pressed with additional load against the reversing means, further increasing the frictional losses.
Therefore, the principal object of the present invention is to eliminate or reduce the component of the friction in the reversal regions that arises from this change in direction of rotation of the rolling elements. A further object is to substantially reduce the total frictional losses in these regions and throughout the system.
According to a central feature of the invention, a linear bearing for continuous longitudinal movement comprises a housing which defines at least one closed roller orbit for accommodating a plurality of rollers, each said roller orbit having an inner surface and an outer surface. Each said roller orbit also comprises a load zone and a return travel zone, which are interconnected at both ends thereof by respective reversal regions. The load zone is defined at least in part by a raceway which is located in the housing adjacent to the load zone for applying a load to rollers when they are accommodated in each said roller orbit, the raceway forming part of the outer surface of each said roller orbit.
According to another important feature of the invention, each roller has a section plane which passes through the center of the roller, perpendicular to its axis of rotation, and the respective section planes of the rollers in the load zone and the rollers in the return travel zone intersect along an axis which extends parallel to the load zone. These two section planes advantageously define an angle of about 15.degree. to 60.degree.. More preferably, the angle is from about 40.degree. to 50.degree..
In another feature of the invention, each of the reversal regions includes a transitional region that is approximately helically curved. The reversal regions may also include two-dimensionally curved regions in which the axes of rotation of the rollers therein are substantially parallel to the axes of rotation of the rollers in the return travel zone.
The above-mentioned problems are solved by these features of the invention. For example, even in the reversal regions, the rolling members can continue to roll in the same direction of rotation as in the load zone. Since the raceway arranged on the housing adjacent to the load zone forms part of the outer surface (see FIG. 2) of each roller orbit, no reversal of the direction of rotation of the rollers necessarily takes place. This avoids the disadvantages of the prior art, in which the raceway of the load zone is arranged on the inner surface (see FIG. 1).
For considerations of space, it is desirable for the rolling members to be brought into and out of the load zone by reversal regions having the features mentioned above, which permit return travel of the rollers to take place in a region close to the load zone and the travel rail.
In order to minimize the total frictional losses in the reversal regions, it is preferable for the rolling elements to return through a return travel zone which is at a specified angle to the load zone, in accordance with the above-mentioned features, which provides a frictionally favorable angle of swing of the rollers with only a small amount of space being required.
The measures described also result in quiet operation of the rolling members. Furthermore, frictional losses, and thus also the consumption of energy, are reduced. All of this results in an increase in the life of the bearing. Furthermore, excellent load-bearing characteristics relative to the small space required and the low weight of the device are obtained.
The passage of the rollers from the load zone into the return-travel zone is frictionally most favorable if, in accordance with one aspect of the invention, a two-dimensionally curved section adjoins an approximately helically curved transitional region and these two sections provide a continuous transfer of the rollers from the load zone into the return-travel zone. This is facilitated by the axes of rotation of the rollers in the two-dimensionally curved section being in the same direction as in the return-travel zone.
Conditions are most favorable with respect to both construction and friction if, in accordance with another feature of the invention, the return-travel zone is oriented alongside the load zone, at an angle thereto of about 15.degree. to 60.degree.; and more preferably about 40.degree. to 50.degree.. In such case, with ordinary reversal radii and roller diameters, a favorable length of the closed roller orbits and optimal use of space are obtained.
The frictionally favorable guidance of the roller orbit in accordance with the invention can be provided not only with one orbit path but also, in accordance with further improved embodiments of the invention, with a larger number of roller orbit paths. For example, four roller orbits may be provided, in which case the axes of rotation of the rollers may advantageously form an X. Such arrangements were not possible with prior art linear bearings, in which the return travel path of the rollers was spaced away frcm and parallel to the load zone within the housing. The prior art arrangements therefore occupied a large amount of space. With X arrangements according to the invention a large reduction in occupied space is achieved, in that the return travel of the rollers takes place as close as possible to the travel rail. Further space is saved in accordance with another feature of the invention, wherein the roller orbits are preferably arranged within the main cross-section of the travel rail.
In order to obtain a bearing which can be easily disassembled for purposes of simple manufacture and inspection, in accordance with another feature of the invention the return travel paths are provided in cages which have openings on one side. When the travel rail is not present the rollers can be removed without difficulty.
Due to the presence of the openings in the cages, however, the rollers might drop out. It is therefore advisable to provide easily removable holding plates by means of which the openings can be completely or partially closed.
Also, in order to prevent the rollers in the load zone from falling out, as might be possible when the travel rail is not present, the holding plates can be provided with holding sections which extend or are bent away from the principal surface of the holding plate, and grip around the rollers. Larger holding sections may be provided on the outsides of the raceway regions and only small ones on the insides.